Just one night before the Carnegie Deli massacre, the two alleged murderers made a creepy preview visit to the crime scene, a witness told jurors in bombshell testimony yesterday.

“I found suspicion in the silences,” witness Luis Peña said of the two tight-lipped visitors. The pair exhibited a “chilling coldness” as they sat on a couch during the less-than-10-minute visit, he insisted, adding, “There was something in the air.”

The testimony backs an important prosecution claim that Sean Salley, 30, and André Smith, 31, cased the place on the eve of their armed drug-heist-turned-triple-murder in a fifth-floor marijuana den above the famed Theater District eatery.

The testimony by the ponytailed Peña – a self-described musical-theater actor and surrealistic painter – was particularly damaging to the case of Smith, who claims he was never at the apartment where the slaughter took place in May 2001.

But Peña’s impact was greatly blunted during cross-examination, when defense lawyers caught him in some apparent exaggerations and got him to admit that cops initially brushed him off as an attention-seeker.

Peña boasted he was “very close” with pot dealer Jennifer Stahl, 39, who lived in the apartment and whose cash and drugs were the target of the heist.

But on cross-examination, he appeared to misstate the days on which she took pot customers and backtracked on how many times he’d been to the apartment in the months before her murder.

Also yesterday, a Bronx grand jury indicted Salley for assault – for punching a jail guard on Rikers Island last Tuesday. The guard needed eight stitches to close the gash in his head. Salley faces an added seven years in prison for the attack in addition to the life sentence he faces in the massacre.